Perhaps it would be better if we qualified terms like 'natural', which mean
different things to different linguists. E.g. palatalization before front
vowels is 'natural' because it reduces articulatory complexity. On the other
hand, there might be 'natural' changes that have little to do with articulatory
complexity. In some technical discussions, 'natural' means little more than
'frequently observed'. There is no single standard by which to measure
naturalness.
It has been asked why relatively less natural configurations persist in
language. For example, why don't all languages eliminate [ki] clusters
via palatalization? First of all, [ki] clusters are not unnatural by virtue
of just a single natural process. You could ease articulation by changing
the vowel to a non-palatalizing back vowel. That move would remove the transi-
tional complexity, but leave you with an 'unnatural' high back unrounded vowel.
This kind of thing happens. Russian {gde} 'where' is historically related to
{kuda} 'whither'. A short [u] dropped between [k] and [d]. Then regressive
voice assimilation stepped in to polish off the resulting cluster. All very
natural, but look at that cluster! So isolated natural changes don't necessar-
ily lead to more natural overall systems.
If a language were to eliminate all unnatural sounds totally, I submit that it
would have no sounds at all. Indeed, this is what one phonological theory--
Stampe's Natural Phonology--takes to be the case at the onset of phonological
acquisition. The infant reduces everything to silence by a process of phonolo-
gical overkill. Phonological acquisition entails modification of the initial
system until the child can pronounce what he/she needs to. The leftover
processes constitute the mature phonological system. If you observe the pro-
gression from babytalk to mature pronunciation, then you see that language
change tends to move in the reverse direction from language acquisition. Or
perhaps you could say that change is a kind of "imperfect learning". Which
brings me to the following recommendation (to be read before Bert Peeters'
Martinet reference, i.e. in chronological sequence): Paul Passy. 1890.
"Etude sur les Changements Phonetiques" Paris: Librairie-Diderot. One of the
earliest works discussing the two great opposing forces in language: ease and
clarity. IMHO, therein lies the answer to why lack of naturalness persists.
Rick Wojcik (rwojcikatc.boeing.com)

I appreciate Michael Kac's distinguishing between possible sounds and
natural sounds. But then 'naturalness' of speech sounds is a rather
tricky issue. Say, the voiced uvular trill in the first sound of the
German word _Rad_ ('wheel') may be difficult to a monolingual English
speaker, but it is by no means unnatural to a native German speaker.
Another example is the 'ch' sound in the Scottish pronunciation of
_loch_. (And in my native Chinese dialect, there is nothing unnatural
about an 'm' immediately followed by an 'ng' in the same word.)
I do not claim that technical linguistic factors do not have a role to
play in sound change, though. Social forces do not counteract
linguistic change. They just have a role to play there.
Tom Lai

I'm glad to see the question of "What causes sound change?"
reopened here for informal discussion, even though I suspect
that the simplicity of the question's form is a large part of
what dooms us to failure in trying to answer it.
The problem of oversimplification is only slightly reduced
by asking separately about the "origination" ("actuation")
and the "propagation" of sound changes.
If for the moment, tentatively, propagation can be satisfactorily
explained simply as people's conscious or unconscious imitation of
a prestige-group's pronunciation, then we have only to explain
the origination problem. But this origination seems elusive:
it occurs somewhere between the random, socially-insignificant,
synchronic variations permitted and ignored by speakers, on one hand,
and the full-fledged rule-governed sound-change on the march
(through society, geography, and/or the lexicon), on the other.
How does a random fluctuation become ruly; when does a ruly change
take on social significance; and what is it before it does that?
The purpose of this note is both to request and to offer:
to ask if anyone has found a metaphor that helps them grasp
that elusive moment when random variation turns into nascent
regular change; and to offer two of my own (as yet whimsical) images
for possible discussion -- (1) the Brownian motion of molecules
in a fluid, and (2) a stampede of wildebeests. Yes, whimsical:
I hereby forbid any reader to treat either one as a solid proposal
at this time.
If a society were purely egalitarian in an impossibly mechanical
way -- with no gradients of prestige -- perhaps language fluctuation
would, like the Brownian motion, never become so organized as to flow
in a particular direction. Conversely, if for example water molecules
had a social pecking-order among them, then perhaps the at-first-random
motion of an influential molecule would be followed by others
to the point of bringing about an eddy current or even a migratory flow
of some volume of water -- analogous to a permanent diachronic
sound change.
What the Brownian motion brings to the question of sound change
is the reminder that the background of synchronic variation is always
present, more so than "we" usually recognize. Given this constant
variation, the origination of a ruly change is not so much a matter of
"initiating" something as it is of _choosing_, from among the available
repertoir of on-going variations, a particular variation to push forward.
But now we have succeeded only in making two unanswered questions
where before there was one: (1) Why (aside from the usual requirements
of maintaining contrasts and intelligibility) does phonological system S
permit synchronic variations V1, V2, and V3, but not V4, V5, and V6?
And (2) why does variation V1 get chosen for pushing forward,
but not V2 or V3?
Meanwhile, we've seen the Family Tree "theory" and the Wave "theory" --
consider now the Wildebeest "theory" of sound change (bearing in mind
the caveat that I know nothing first-hand about real wildebeest behavior).
We might say that a heard of wildebeest -- or a large flock of starlings
or school of fish, for that matter -- is made up of individuals who move
under the combined influences both of individual-internal and of social
forces. Each wildebeest (I speculate) moves partly at random, as required
by grazing, but the movements of a socially influencial member of the herd
might be magnified as he or she is followed and imitated by socially more
subordinate wildebeests. The point here, as with the Brownian motion,
is that all wildebeests are in motion at all times, but that social forces
may channel and encourage some of those motions and suppress others.
The analogy with sound change is, I presume, obvious.
One more question, and I'll close. Kiparsky, in his 1970 essay
"Historical Linguistics" discusses the difference between "competence theories"
(in Lyons, ed.; not his 1971 essay of the same title, in Dingwall, ed. --
chapter 3 of K's 1982 book _Explanation in Phonology_)
vs. "performance theories" of sound change (referring to where change
is thought to originate). H. Anderson, in a 1973 article in _Language_,
distinguishes between "evolutive" and "adaptive" changes.
My question: What does anyone today think of either or both
of these dichotomies? Are they valid?
Lee Hartman, Southern Illinois University at Carbondale, ga5123siucvmb.bitnet